I too had chronic bronchitis for a whole year, despite a very healthy diet and comprehensive supplementation. At the end I threw the towel, and went for 5 month to a South Indian beach to try let it heal with lots of sea-air, sunshine and Ayurvedic herbals. It worked for me, though first i suffered a severe UTI and 1 whole months of fevers (along with diarhea, vomiting; probably thypoid fever). Later it was diagnosed a COPD1, though asymptomatic since.
I've had ME/CFS for decades. Around 10 years ago I got a cold and cough. The cold went but the cough didn't. I'd never cough during the night but as soon as I got up in the morning, and got moving the coughing would start. After some months went to the doctors and he gave me an inhaler. Never did any good whatsoever. I too must of had this cough a couple of years. I went online to look for possible answers. I read something about vitamin D, so got some. Took my first one just before bed. Got up next morning. A miracle. The tickly feeling in my throat had disappeared!! My cough had gone. If only I could find a miracle that simple for my ME/CFS.
Like you, I've had a nagging, persistent cough since an incredibly bad bout of flu in late 2014. It finally went away, but came back with a vengeance after Mar 2020 mild COVID.
Here;s what I found, thru a post right here on a PR thread, and I wish I could remember the thread or the poster because I owe him/her an enormous debt of gratitude.
Thru something they linked on that post, I stumbled onto SPIKENARD ROOT, FRESH EXTRACT, and being desperate, decided to risk the $45.00 for a 4 oz bottle, plus $10.00 s/h .... the results were astonishing. Within 1 full day of taking a couple of doses, my cough had dramatically receded. By the 4th or 5th day, it was, for all practical purposes, GONE !!! I could sleep thru the night without being awakened by a dry, wracking cough. I could breathe without choking. It was a miracle.
I don't know if it'll work the same way for you, but here's a link to VOYAGE BOTANICA, the only herb company I've found that has FRESH Spikenard Root (aralia racemosa) extract:
EDIT ..... As an afterthought, I thought that I'd mention that I've been taking med/large doses of D3 for 2-plus years, and it had no apparent effect on my cough. And with all due respect to Mercola, I'd be cautious with some of his recommendations.